Investigations are underway to determine how the cockpit door on a packed Tigerair flight sprang open abruptly when the plane touched down at Melbourne Airport last week.

The securing of cockpit doors is an airline safety essential and has been since the ‘9/11’ terrorist attacks on New York in 2001, when terrorists gained access to cockpits, took over the planes and flew them on suicide missions.

There was no suggestion of any foul play aboard Tigerair flight TT472 from Adelaide to Melbourne – but a passenger said the door swang open as the plane touched down, Melbourne’s Age reported.

The passenger said the door remained ajar while the aircraft taxied towards the terminal.

Tigerair Australia confirmed a “minor incident” had taken place – a reference to the door opening – on an A320 carrying 180 passengers following a flight to Melbourne.

“This was an isolated incident, however the airline is currently reviewing the matter as per standard procedure,” Tigerair Australia spokeswoman Vanessa Regan said.

“As the matter is subject to review by the airline, we are unable to comment further on the details at this time.”

Regan said the safety and security of passengers and staff was Tigerair’s first priority and the airline maintained “strict and comprehensive procedures” to ensure “the highest levels of safety and security” at all times during flight.